In a case of using semiconductor nanoparticles that emit fluorescence as a fluorescent labeling agent, particles having higher luminance per particle are desired, because sensitivity becomes higher as luminance per particle becomes higher.
As semiconductor nanoparticles, ones of groups II-VI, and groups III-V are widely known. However, in the current situation, luminance per particle is far too low for these semiconductor nanoparticles to be used as a fluorescent diagnostic agent.
On the other hand, generally, core semiconductor nanoparticles alone have much lower particle luminance than that of semiconductor nanoparticles having core/shell structures. By using a semiconductor material having a larger band gap than core particles as a shell, a quantum well is formed to produce a quantum confinement effect, significantly increasing luminance.
Accordingly, a method is conceived, in which core/shell semiconductor nanoparticles are assembled, in order to increase luminance.
However, by assembling the semiconductor nanoparticles in a highly concentrated state, the particles become too close to each other to cause concentration quenching. Here, the concentration quenching occurs because the core; shell particles contact with each other to cause electron transfer, deteriorating the quantum confinement effect.
In the meantime, methods for synthesizing semiconductor nanoparticles such as the ones mentioned above in an aqueous solution and a non-aqueous solution have been developed. However, immediately after the synthesis, semiconductor nanoparticles synthesized in the solution degrades in light emitting properties due to gradual aggregation or the like of the particles. Further, the nanoparticles synthesized in the non-aqueous solution in particular are weak in moisture, rapidly degrading fluorescence properties when coexisting with a minute amount of moisture. Still further, there has been a problem that the nanoparticle solution is difficult to be applied as it is as a material from an engineering aspect.
Therefore, a method is proposed, in which the semiconductor nanoparticles are confined in a form of being dispersed and fixed in a matrix such as transparent glass or the like, so that the high luminance properties thereof can be exerted for a long period of time under various environments, and the nanoparticles become suitable for being applied from the engineering aspect.
For example, in Non-Patent Literature 1, a technique is disclosed, in which surfaces of silica beads are processed with silane coupling to amino functionalize the ends thereof, and the silica beads are reacted with carboxyl-terminated semiconductor nanoparticles to bond the two together by amide bonding. However, quantum dots only accumulate on the surfaces of the silica beads; therefore the semiconductor nanoparticles cannot be accumulated so much in respect of concentration.
Furthermore, for example in Patent Literature 1, a glass phosphor is disclosed, in which semiconductor nanoparticles are dispersed and fixed, and formed by combining a reverse micelle method and a sol-gel method in which a mixture of organic alkoxysilane having an organic functional group with good adsorption properties of molecular terminals to semiconductor nanoparticles and alkoxide is used as a glass precursor. However, degradation of the luminance properties is observed, which is caused by influence during the sol-gel reaction. Also, the method involves a presence of hydrolysis products of the organic alkoxysilane and the alkoxide, which lengthen gaps between the semiconductor nanoparticles. This causes a problem that the semiconductor particles cannot be accumulated so much in respect of concentration.